1. Field of the Invention
The present inventions relates to a fan assembly, and in particular, to a fan and an impeller thereof with higher strength and better performance.
2. Description of the Related Art
Electronic devices generally produce heat during operation, and thus, a heat-dissipating device or a fan assembly is required to dissipate the excess heat. Since the demand for heat-dissipation has increased, fans must offer optimal performance. A conventional impeller 10a of a fan is shown in FIG. 1A, including a plurality of blades 21 and a hub 22. The blades 21 encircle the hub 22. The hub 22 contains a motor (not shown) therein. The blades 21 are disposed in a frame 20 and connected to the hub 22 via a connecting portion 24 extending from a bottom of the hub 22. A gap 23 is formed between the hub 22 and the blades 21, above the connecting portion 24.
As shown in FIG. 1B, airflow enters the gap 23 to contact the blades 21 and flows in a direction shown by the arrows and dashed lines. Due to space limitations imposed by the other elements in the fan, a conventional way to increase the rotational speed of the motor is to increase the height H of the motor or the hub to approximately the same height as the blades 21. The motor, however, almost entirely blocks the inlet such that the airflow is unable to smoothly flow through the gap 23 between the blades 21 and the hub 22. Thus, the contact area between the airflow and the blades 21 is insufficient. Because the inlet area is reduced, the performance is also reduced. Furthermore, the conventional fan requires the gap 23, which weakens the strength of the impeller.
As mentioned above, the conventional fan needs to increase the height of the motor in order to increase power and rotational speed, but the length of the blades 21 must also be increased to increase the airflow contact area. The longer the blades 21, however, the weaker the strength of the impeller, that is, the long blades 21 are easily deformed.
Another conventional impeller 10b adds a rib 25 to increase the strength of the blades 21, as shown in FIGS. 2A and 2B. Each blade 21 of the impeller 10b is divided into upper and lower partial blades 21a and 21b. The rib 25 is disposed between the upper and lower partial blades 21a and 21b and connected to the hub 22. Thus, the blade structure can be strengthened by the rib 25. The rib 25, however, may interfere with the airflow, which must travel around the rib 25 to enter the gap 23, thus causing turbulence. Furthermore, the amount of inflow is reduced due to insufficient contact area between the airflow and the blade 21. As a result, the motor is unable to increase the rotational speed.
Hence, the above method is still unable to satisfy the demands of both structural stability and fan performance.